Selective Pd-Catalyzed Monoarylation of Small Primary Alkyl Amines through Backbone-Modification in Ylide-Functionalized Phosphines (YPhos)

Ylide-substituted phosphines have been shown to be excellent ligands for C–N coupling reactions under mild reaction conditions. Here we report studies on the impact of the steric demand of the substituent in the ylide-backbone on the catalytic activity. Two new YPhos ligands with bulky ortho-tolyl (pinkYPhos) and mesityl (mesYPhos) substituents were synthesized, which are slightly more sterically demanding than their phenyl analogue but considerably less flexible. This change in the ligand design leads to higher selectivities and yields in the arylation of small primary amines compared to previously reported YPhos ligands. Even MeNH2 and EtNH2 could be coupled at room temperature with a series of aryl chlorides in high yields.

已有研究证实，叶立德取代膦（Ylide-substituted phosphines）是温和反应条件下C-N偶联反应的优良配体。本文报道了叶立德骨架上取代基的空间位阻对催化活性影响的相关研究。我们合成了两款新型YPhos配体，分别带有大位阻邻甲苯基（pinkYPhos）与均三甲苯基（mesYPhos）取代基；相较于其苯基类似物，这两款配体的空间位阻略大，但柔性显著更低。与此前报道的YPhos配体相比，该配体设计的调整使得小位阻伯胺的芳基化反应具备更高的选择性与反应收率。即便甲胺（MeNH₂）与乙胺（EtNH₂），也可在室温下与一系列芳基氯发生偶联反应，且获得高收率。